When the stimulable phosphor is exposed to radiation such as X-rays, it absorbs and stores a portion of the radiation energy. The stimulable phosphor then emits stimulated emission according to the level of the stored energy when the phosphor is exposed to electromagnetic wave such as visible light or infrared rays (i.e., stimulating light).
A radiation image recording and reproducing method utilizing the stimulable phosphor has been widely employed in practice. The method employs a radiation image storage panel comprising the stimulable phosphor, and comprises the steps of causing the stimulable phosphor of the storage panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with a stimulating light to emit stimulated light; and photo-electrically detecting the emitted light to obtain electric signals giving a visible radiation image. The storage panel thus treated is subjected to a step for erasing radiation energy remaining therein, and then stored for the use in the next recording and reproducing procedure. Thus, the radiation image storage panel can be repeatedly used.
The radiation image storage panel (often referred to as stimulable phosphor sheet) has a basic structure comprising a substrate and a stimulable phosphor layer provided thereon.
The phosphor layer is generally formed by coating a dispersion of phosphor particles in a binder solution on the substrate and drying the coated dispersion on the substrate, and therefore comprises a binder and phosphor particles dispersed therein.
It is desired that radiation image storage panels used in these methods have sensitivity as high as possible and further can give a reproduced radiation image of high quality (in regard of sharpness and graininess).
It is known that a radiation image storage panel having on a substrate a stimulable phosphor film prepared by vapor deposition (or vapor-accumulating method) such as vacuum vapor deposition or sputtering gives a reproduced radiation image with high sensitivity as well as high sharpness.
Japanese Patent Publication No. 6-77079 describes a radiation image storage panel in which a stimulable phosphor film is formed by vapor deposition to have a fine block structure.
Japanese Patent No. 3,130,632 describes a radiation image storage panel having a stimulable phosphor layer which shows a ratio of a strength I2 of the second diffraction peak observed in an X-ray diffraction pattern and a strength I1 of the first diffraction peak observed in the same X-ray diffraction pattern satisfying the condition of I2/I1<0.3 shows a high radiation sensitivity and gives a radiation image of high image quality. In the working examples, RbBr:Tl has a first diffraction peak I1 on a (422) face, or a (220) crystal face, or a (200) crystal face.